I have now found a clear image of Princess Alice of Albany from the 1911 coronation which shows that she too wore a coronet with fleurs de lys rather than strawberry leaves.

If I have understood Boffer's train of thought correctly that was in keeping with the rules in 1911, but Boffer's line of argument does not take into account the fact that the Duke of Connaught's son was holding a coronet with crosses patee and strawberry leaves in 1911.